1. Field of the Invention
The present invention relates to a fuel injection valve for an internal combustion engine. More particularly, the invention relates to a fuel injection valve having two injected fuel paths and improved fuel atomizing.
2. Description of the Related Art
Electro-magnetic fuel injection valves having two injected fuel paths are known as taught in, for example, Japanese Utility Model Publication SHO 61-198574. Further, techniques of atomizing a fuel by letting an air stream collide with the fuel are known as taught in, for example, Japanese Utility Model Publications SHO 59-172267 and SHO 61-164470, though the fuel injection valves of the publications are ones with a pintle type needle valve which are not the type used in the present invention.
More particularly, Japanese Utility Model Publication 61-198574 discloses a basic structure of a fuel injection valve of the same type as the present invention, that is, a fuel injection valve including an injector body having a single fuel injection hole and an adapter, coupled to the injector body, having a dead volume portion, two injected fuel paths communicating with the dead volume portion, and a dividing wall located between the injected fuel paths. In the fuel injection valve, the fuel injected from the fuel injection hole flows in the dead volume portion in a slug-like pattern and then is divided into two portions by the dividing wall. Each of the two portions passes through each injected fuel path and is injected into an intake port of the engine. The fuel is injected into the intake port substantially in a slug-like pattern, because the fuel is not effectively atomized in the adapter Though the dividing wall opposes the fuel injection hole, the top surface of the dividing wall is upwardly edged for the purpose of making the flow resistance as small as possible. As a result, the top surface of the dividing wall cannot let the fuel collide with the top surface at a nearly right angle and cannot atomize the fuel. The fuel injection valve does not use a technique to let an air stream collide with the fuel for atomizing the fuel.
Though the technique using an air stream for atomizing a fuel is taught in Japanese Utility Model Publication SHO 59-172267, the fuel injection valve disclosed in the publication relates to a fuel injection valve with a pintle type needle valve which has a too different fuel injection mechanism to attempt to apply the mechanism to a fuel injection valve having no pintle type needle valve. In more detail, in the fuel injection valve having a pintle type needle valve, the fuel is injected through an annular clearance defined between the needle valve and an inside surface of a fuel injection hole and flows in a cone-like pattern from the beginning, while in the fuel injection valve without a pintle type needle valve, the fuel injected from a fuel injection hole flows in a slug-like pattern. Even if the technique of letting the air collide with the fuel disclosed in the publication could be applied to a fuel injection valve having no pintle type needle valve, a high fuel atomizing effect could not be obtained, because the air collides with fuel which has not collided with a surface of the adapter and thus has not been promoted in atomizing.
Japanese Utility Model Publication SHO 61-164470 also discloses a fuel injection valve with a pintle type needle valve. In the fuel injection valve, the air injected from air injection holes does not operate to atomize the fuel but operates only to cause a swirl in the adapter. Further, in the publication, there is no suggestion of letting the fuel collide with a top surface of the dividing wall, because the lower end surface of the pintle type needle valve is located close to the top surface of the dividing wall, and the fuel cannot collide with the top surface of the dividing wall.
As will be apparent from the above discussion, though some of the prior art fuel injection valves having a pintle type needle valve include air injection holes, the techniques of the air injection holes are difficult to apply to a fuel injection valve having no pintle type needle valve, especially to a fuel injection valve having a fuel injection hole for injecting fuel in a slug-like pattern and two injected fuel paths for letting the fuel injected from the fuel injection hole pass therethrough. Thus, the fuel atomizing characteristic of a fuel injection valve having no pintle type needle valve is problematic. In more detail, the fuel injected from the fuel injection valve comprises two slug-like patterns of fuel which is composed of the flow of a lot of fuel drops having a comparatively large drop diameter. Such fuel flow with large sized fuel drops is likely to cause insufficient fuel evaporation in a cylinder of the engine as well as insufficient mixing of the fuel with air in the intake port and the cylinder As a result, carbon, deposits around the spark plugs and an increase of HC and CO gases in the exhaust gas will occur.